UPDATE 7/3/06: After some discussion, these are some of the answers that have come up.

1.) The Dark Avatar Spirit represents nearly pure Negative Chi, or Yin. Therefore Aang's Avatar Spirit represents nearly pure Positive Chi, or Yang. For the definitions of Yin and Yang, see this link for wikipedia.org. How would you decide this splitting to have originated, how would this have affected the personalities of their reincarnations,??and how in the series would this balance be restored eventually?

While the origin is still under discussion, for this version I've decided that the origin of the Dark Avatar Spirit is the same as the Light Avatar Spirit.??Basically, the Avatar Spirit was the result of a kind of peace agreement between the patron Spirits of the 4 Nations, which before the Avatar's creation lived in constant warfare ("Cave of.Two Lovers"). Unfortunately, they could not instill everything into a single person, so they split it into two parts, one Positive Chi, the other Negative Chi. While the Avatar of Light was much beloved of the people and sought peaceful and long lasting solutions to the conflicts, the Dark Avatar sought to undo and create chaos, something that the Spirits had sought to end. War and chaos reigned as the Dark Avatar brought??the worst of humanity??back to the world with each reincarnation, the best the Light Avatar could do was to put out the??conflicts as they appeared, but it was an unending, grinding battle. Eventually, tapping into the pure Chi essences revealed new forms of bending that eventually did as much damage to the bender as it did the opponent. The Balance was at risk of coming undone and humanity was on the road toward self-destruction. The Spirits decided to remove the Avatar Spirit's darker half and??cast it from the world, imprisoning it in a prison made up of all four elements. This comet eventually slowed and began a spiral back toward the world, a journey that would take tens of thousands of years.

2.) In order to up the ante, so to speak, the Dark Avatar would have to have a unique form of bending to set??itself above other benders and Aang himself initially, hence Shadowbending. I believe the real world martial art this could be based on is Tien Shan Pai, the description of which can be found at this link on wikipedia.org.

As for Aang, he should learn the??opposite form of bending which does not outclass Shadowbending, but merely cancels it out, Lightbending. Lightbending could be based on the real world martial art of WingTsun, the description of which can be found at this link, from wikipedia.org.

The question is how should these artforms be visualized? Should shadowbending be like, for example, like Teen Titan's Ravens powers? Could lightbending be like??typical anime energy attacks (like Ryoko from Tenchi or the various characters from Dragonball)? Another question is how should the Dark Avatar spread the art of Shadowbending to other benders? Would it be taught or merely a??fragment/seed??of its spirit, with all the skill built in? Would defeating a shadowbender free them from the fragment's influence? How would it affect their native elements?

This part of the theory is still under discussion.

3.) Finally, how would the Dark Avatar be introduced after Season 3? I have stated that it should be imprisoned in Sozen's Comet and that it should possess someone defeated by Aang in the past and would be willing to give up their will for the power of the Dark Avatar. I feel Azula is a prime candidate for this purpose, especially if she is defeated by the end of Season 3, preferably by Zuko via Agni Kai.

Azula has proven to be a primary candidate as the new Dark Avatar. As the Dark Avatar Spirit is??not truly??evil, it's power would make Azula a force to be reckoned with. It also seems appropriate to have Azula be scarred via Agni Kai by Zuko, an ironic twist.

I really disagree with the Shadow/Light bending idea. The ideas that seems to be proven in the series is that the Bending styles are all equal. Each one can be used for good or evil, neither one is better or worse than the other. It is the skills of the user and certain outside factors that determines who wins a battle.??Shadow/Light bending as you state it seems to say that one style is pure good and the other is pure evil. That doesn't seem to fit with the other bending styles.

??It seems to me that it would less be a new version of bending, but rather an new way to look at current bending practices. The ideas that the Dark Avatar seems to be promoting is that of superiority, rather than that of equality that the Avatar promotes. (Think about Zhao's speech in "The Blue Spirit" compared to the lecture given by Iroh in "Bitter Work").

??I see the Dark Avatar giving a boost in the power of Bending of others, giving them a false??sense of their own superiority. As their ego grows with the feedback of their own increased??power, they reject the Avatar's wisdom of equality and balance with nature. It could be that the Dark Avatar would preach to the benders that their element is the best, and that if they can work with the inferior other elements that follow the Dark Avatar, they would gain control of the new world that Dark Avatar is creating. As they people give in to the idea of the superiority of their element/people, the Dark Avatar gains a link to their soul which is hard to break.

??I can see the Dark Avatar trying to influence each country with this docturne. Chin could have started his control of the Earth Kingdom as part of a plan for world domination and superiority of the Earth Element. Only to be accidentlt stopped by Kyoshi. (Avatar Day) I can see this occuring in all four counties with Water, Earth and Fire listening to it from time to time. The Air Nomads don't seem to be the type to follow a world domination type, I see them locking up these characters as unbalanced.

Just an alterntive idea I had to the Shadow/Lightbeing as that didn't make much sense to me from what the show has gone so far.